> I'm missing why you would ever want the Lucene index in HDFS for > reading.
The Lucene indexes are written to HDFS, but that does not mean you conduct search on the indexes stored in HDFS directly. HDFS is not designed for random access. Usually the indexes are copied to the nodes where search will be served. With http://issues.apache.org/jira/browse/HADOOP-4801, however, it may become feasible to search on HDFS directly. Cheers, Ning On Mon, Mar 16, 2009 at 4:52 PM, Ian Soboroff <ian.sobor...@nist.gov> wrote: > > Does anyone have stats on how multiple readers on an optimized Lucene > index in HDFS compares with a ParallelMultiReader (or whatever its > called) over RPC on a local filesystem? > > I'm missing why you would ever want the Lucene index in HDFS for > reading. > > Ian > > Ning Li <ning.li...@gmail.com> writes: > >> I should have pointed out that Nutch index build and contrib/index >> targets different applications. The latter is for applications who >> simply want to build Lucene index from a set of documents - e.g. no >> link analysis. >> >> As to writing Lucene indexes, both work the same way - write the final >> results to local file system and then copy to HDFS. In contrib/index, >> the intermediate results are in memory and not written to HDFS. >> >> Hope it clarifies things. >> >> Cheers, >> Ning >> >> >> On Mon, Mar 16, 2009 at 2:57 PM, Ian Soboroff <ian.sobor...@nist.gov> wrote: >>> >>> I understand why you would index in the reduce phase, because the anchor >>> text gets shuffled to be next to the document. However, when you index >>> in the map phase, don't you just have to reindex later? >>> >>> The main point to the OP is that HDFS is a bad FS for writing Lucene >>> indexes because of how Lucene works. The simple approach is to write >>> your index outside of HDFS in the reduce phase, and then merge the >>> indexes from each reducer manually. >>> >>> Ian >>> >>> Ning Li <ning.li...@gmail.com> writes: >>> >>>> Or you can check out the index contrib. The difference of the two is that: >>>> - In Nutch's indexing map/reduce job, indexes are built in the >>>> reduce phase. Afterwards, they are merged into smaller number of >>>> shards if necessary. The last time I checked, the merge process does >>>> not use map/reduce. >>>> - In contrib/index, small indexes are built in the map phase. They >>>> are merged into the desired number of shards in the reduce phase. In >>>> addition, they can be merged into existing shards. >>>> >>>> Cheers, >>>> Ning >>>> >>>> >>>> On Fri, Mar 13, 2009 at 1:34 AM, 王红宝 <imcap...@126.com> wrote: >>>>> you can see the nutch code. >>>>> >>>>> 2009/3/13 Mark Kerzner <markkerz...@gmail.com> >>>>> >>>>>> Hi, >>>>>> >>>>>> How do I allow multiple nodes to write to the same index file in HDFS? >>>>>> >>>>>> Thank you, >>>>>> Mark >>>>>> >>>>> >>> >>> > >
